The present invention relates to an optical apparatus having at least one radiation deflector for measuring electromagnetic radiation emitted from at least two radiation sources.
Apparatus of this type are known, for example, in conjunction with rapid heating furnaces for the thermal treatment of semiconductor substrates for manufacturing semiconductor chips. In order to be able to measure the parameters and characteristics, such as the temperature, the emissivity, the reflectivity, the transmissivity and/or the characteristics or thickness of a layer that is to be applied to the semiconductor substrate during the thermal treatment, the radiation coming from the semiconductor substrate is measured as is the radiation that is emitted from the radiation sources provided for heating up the semiconductor substrates. By comparing the two measured radiation values it is possible to differentiate between the radiation emitted from the semiconductor substrate and the reflected radiation. Apparatus and methods of this type are known, for example, from U.S. Pat. No. 5,490,728, where light lines are used in order to guide the respective radiation, and in particular also the radiation given off by the radiation sources, to radiation detectors. The inlet openings of these light lines, however, have a large and undefined opening angle, so that also a relatively great amount of background radiation is taken in and falls upon the radiation detector. As a consequence, the measured valuesxe2x80x94if at allxe2x80x94indicate little and are not specific with respect to the actual radiation coming from the radiation sources.
Furthermore, from DE 93 12 231 an apparatus for measuring UV radiation is known where a photo diode for measuring UV radiation emitted from a radiation source is provided in a cylindrical housing having an opening. The opening is partially closed off by a restrictor that forms a radiation channel.
Reference is further made to DE 31 29 065, which discloses a device for the photoelectric monitoring of a flow medium, where a light source and a direct light receiver disposed opposite the light source are provided and the light receiver is disposed in a receiver bus having a light line channel. DE 39 08 627 furthermore discloses a multi-element infrared detector where in front of each detector element there is disposed a light line in the form of light conducting channels formed in a channel plate, with the dimensions of the channels effecting a dampening of radar radiation. In addition, disposed in front of the channel plate is a shutter or aperture plate which has openings that are aligned with the light conductive channels and have non-reflective inner surfaces. FR 2 707 005 finally discloses a semicircular photo detector arrangement where light conducting channels are disposed in a semicircular carrier member, and a respective photo detector is provided at the ends of the light channels.
It is therefore an object of the present invention to provide an optical radiation measurement apparatus which with straightforward means enables a substantially more precise determination of the electromagnetic radiation emitted from the radiation sources.
Starting from an optical radiation measurement apparatus of the aforementioned general type, this objective is inventively realized by separate radiation channels formed in a channel member for the radiation path between the radiation sources and the radiation detector, which is common for the radiation sources. The radiation channels can thereby be designed very precisely to the radiation source, so no, or only an insignificant portion of, background radiation, which would falsify the measurement result, strikes the radiation detector. As a result, the parameters, characteristics and intensities of the electromagnetic radiation emitted from the radiation sources can be determined significantly more precisely and more reliably.
Pursuant to one particularly advantageous specific embodiment of the invention, the radiation channel has a cross-sectional shape that corresponds to the shape of the radiation source. Due to this shape of the channel cross-section, and the dimensions thereof, a precise adaptation of the radiation channel to the radiation source is possible, so that independently of the shape of the radiation source the background radiation can be reliably masked out.
It is particularly advantageous if the radiation channel has a cross-sectional shape that permits a radiation passage to the radiation detector even if the radiation source deviates from the ideal position. As a result of such a formation of the channel, mechanical modifications or deviations in position of the radiation source, for example a lamp filament, which occur, for example, by vibrations, being out of adjustment, or deformations, for example during the heating process, are not reflected in signal alterations that could otherwise adversely affect the measurement result and the evaluation.
It is particularly advantageous if the radiation channel, or at least one wall of the radiation channel, is structured, for example having a wavy, grooved or corrugated, or irregular wall structure. As a result, the radiation that does not enter parallel to the axis of the radiation channel, in other words which does not originate from the radiation source, is also not guided by reflection upon the radiation detector, but rather is adsorbed. The structured channel wall therefore additionally contributes to undesired and undefined background radiation and scatter light from not falling upon the radiation detector and thereby falsifying the measurement results.
Very advantageous is furthermore an embodiment of the invention pursuant to which the radiation channel has at least one mechanism for altering the cross-sectional area of the radiation channel. By altering the cross-sectional area of the channel, the intensity, with which the radiation given off by a radiation source strikes the radiation detector, can be adjusted, which is especially advantageous if pursuant to a further specific embodiment of the invention, where a number of radiation sources are present, the relationship of the radiation of the respective lamps that strikes the radiation detector can be adjusted relative to one another by altering the cross-sectional area of the respective channel. A particularly straight forward mechanism for altering the cross-sectional area of the channel, and hence of the radiation intensity that strikes the radiation detector, is a screw that can be screwed into the radiation channel transverse to the direction of radiation. However, a variable aperture can also be used.
With some rapid heating systems for the thermal treatment of semiconductor substrates, cool air is blown in between the radiation sources in order to cool some of the elements, for example a reaction chamber. However, due to this cool air flow turbulances occur between the radiation channels and the individual radiation sources and leads to fluctuations in intensity. In order to avoid these fluctuations in intensity, the channel member, with the radiation channel or channels, extends up to the radiation source or sources.
Pursuant to one preferred specific embodiment, the radiation channel can be extended by at least one light transmissive intermediate element that extends the radiation channel and is disposed between at least one outlet opening of a radiation channel and an associated radiation source, without the channel body having to be guided to just before the radiation source. In this connection advantageously an intermediate element that in common extends a plurality of radiation channels is provided. Pursuant to one preferred embodiment of the invention, a quartz or sapphire rod is used for the extension, with which reflections are to the greatest extent possible suppressed at the inner walls so that only the light coming directly from the radiation source strikes the detector.
Pursuant to one particularly advantageous embodiment of the inventionxe2x80x94as already mentionedxe2x80x94a plurality of radiation sources are disposed next to one another, and the channel member, for each radiation source, has a separate radiation channel that extends to the common radiation detector. The radiations of the individual radiation sources, accompanied by the exclusion of background radiation and reciprocal influence, are thereby reliably guided to the common radiation detector, thereby increasing the precision of measurement. If the radiation sources are, for example, individual lamps that are disposed next to one another in a row in the form of a lamp bank, as is the case, for example, with rapid heating apparatus for the thermal treatment of semiconductor substrates, the channels are formed in a fan-like fashion in the channel member between the lamps and the common radiation source.
Since the lamps are essentially disposed in a row, pursuant to a further embodiment of the invention a cylindrical lens is disposed between the ends of the radiation channels that face the radiation detector and the radiation detector, with the lens focusing on the radiation detector the radiation of the individual radiation sources that in a fan-like fashion feeds the radiation detector.
The inventive radiation measurement apparatus can be used with great advantage in conjunction with a rapid heating furnace for the thermal treatment of semiconductor substrates.